My cats know that the office chair at the computer is the best place in the house to sit. It must be, because I spend so much time in it! Sometimes there are two cats, which leaves little room for me. Yasmine at Cat vs Human knows exactly how it is. Link

A simple solution: purchase another office chair. As the one at the keyboard is considered "The Chair Of Power", simply allow said cat to occupy it, and go to sleep. Then roll it aside and replace. One must wait until the cat is asleep, as if awake, they will often jump to the new one. Remember, it is a sin to waken a slumbering cat. This is THE LAW.